Glowing Bank 2 Precat

[clairejeep]

Hi everyone,

My jeep (04 4.0L) has been having some issues lately. It started with some misfires, which I believe I have fully solved now from replacing the coil rail and plugs. Then, I noticed my bank 1 precat was glowing and definitely clogged, accompanied by a P0171 code, which I had chalked up to me not fixing the misfires in time, so I went ahead and replaced all 3 cats and the bank 1 upstream O2 sensor on the jeep.

That seems to have solved my bank 1 precat glowing red and the p0171 code, but I noticed after my last drive that the bank 2 precat is now glowing, the jeep was taking a little more effort than usual to get above 65 mph, and I had 2 new codes: P0174 and P0161, which suggests to me that I definitely have a faulty bank 2 downstream sensor and may have a faulty bank 2 upstream sensor. I've ordered the replacement sensors and will install them once they arrive, but I wanted to get y'all's opinion on what the issue is likely stemming from.

As an additional note, which may be unrelated or even normal, I noticed on my last trip across the country that when I had my cruise control set to 80 on the mountain highways, the vent settings (feet vs. face vs. defrost) would not change until I backed off of the engine power a little, so maybe that indicates a possible vacuum leak, although I have not been able to find any vacuum leaks under my hood.

In summary, do y'all think this is likely to be an O2 sensor issue, or are there other potential causes I should be ready to look into after replacing my sensors? I don't think it's clogged cats at this point because all three are brand new.

 

[macleanflood]

I wouldn't condemn an O2 sensor until I looked at live ODB data and voltages. Gross simplification but a "good" O2 sensor typically ranges below.9v.

And while you're at it I'd look at your fuel trims and check your fuel pressure. Wonder if you're running lean.

You can check live ODB data with a $30 Bluetooth ODB dongle and the free app Torque Lite.

-Mac

 

[JKP]

The AC issue is due to a lack of vacuum. Check for vacuum hoses that have come off the intake, cracked elbows, cracked vacuum lines. Also check the line that goes through the firewall on the passenger side to the AC controls.. A vacuum reservoir is under the battery as well.

This may also be causing the lean code.

Sounds like the heater circuit is shot on the lower O2. Also check the O2 wiring.

 

[GoldenGorilla]

As an additional note, which may be unrelated or even normal, I noticed on my last trip across the country that when I had my cruise control set to 80 on the mountain highways, the vent settings (feet vs. face vs. defrost) would not change until I backed off of the engine power a little, so maybe that indicates a possible vacuum leak, although I have not been able to find any vacuum leaks under my hood.

Definitely hop on those issues quickly so you don't melt your new cat. I normally see the S1 above pre-cat sensors in the 0.05-0.85 mV range with the system desired O2 voltage at 0.490V. They oscillate, but the pattern is not like a sine wave. S2 sensors follow a little behind in the scan but in the same ranges.

Above 1V or at 0.0V you've got a bad sensor.

As for the vacuum leak, a pressurized smoke tester is really helpful for this. It's easiest to plug it in to the vacuum line that goes from the intake manifold to the brake booster and then just check everywhere on the intake side. You'll see some smoke come past the IAC valve in the intake which is normal. But anything coming off the manifold, injectors or any of the vacuum tubing needs to be addressed. Don't forget to turn the smoke connection around and check the brake booster for vacuum leaks, though people tend to notice the lack of braking power. Sounds like you're making progress. Good luck.

 

[clairejeep]

Thanks for the help! As I feared, the new sensors didn't fix the engine running stupid rich, and I couldn't find any vacuum leaks, so now I'm thinking it's probably an exhaust leak somewhere. I did used to live in Wisconsin, so maybe the road salt rotted out part of the manifold. The downstream O2 sensor definitely needed to be replaced though, since it was warped and completely filled with what looked like carbon - so at least the heater circuit issue is fixed now.

 

[clairejeep]

I wouldn't condemn an O2 sensor until I looked at live ODB data and voltages. Gross simplification but a "good" O2 sensor typically ranges below.9v.

View attachment 665480

And while you're at it I'd look at your fuel trims and check your fuel pressure. Wonder if you're running lean.

You can check live ODB data with a $30 Bluetooth ODB dongle and the free app Torque Lite.

-Mac

My fuel trims are around 32% on bank 2 vs. 3% on bank 1.

 

[macleanflood]

Yeah you should be under ten...3 percent is good...32...not so much...

-Mac